1. Field of the Invention
This invention relates to a throttle control system and method for an internal combustion engine as well as an engine control unit, for controlling the degree of opening of a throttle valve arranged in an intake system of the engine.
2. Description of the Prior Art
Conventionally, a throttle control system of this kind has been proposed in Japanese Laid-Open Patent Publication (Kokai) No. 10-176548. In this throttle control system, when the amount of variation in the degree of opening of the throttle valve per unit time period has continued to be equal to or smaller than a predetermined value for a predetermined time period, with the duty factor of current flowing through a motor for actuating the throttle being equal to or larger than a predetermined value, it is determined that the motor is undesirably locked, and an electronic throttle control system is caused to go down. Further, the above predetermined time period set in the determination is set to a larger value when the temperature in the vicinity of the throttle valve is equal to or lower than a predetermined temperature. This is to cause the throttle control system to wait for a longer predetermined time period before execution of the determination for prevention of an erroneous determination, since when the ambient temperature of the throttle valve is low, there is a possibility that the motor is locked due to the freezing of the throttle valve itself or component parts associated therewith (hereinafter simply referred to as xe2x80x9cthe freezing of the throttle valvexe2x80x9d) which causes the throttle valve abuts against frozen ice to make the valve immovable, and in such a case, the frozen ice can be melted with a rise in the engine temperature to thereby restore the throttle valve to its normal operating condition.
However, the proposed conventional throttle control system suffers from the following problems: There can be a case where frozen ice is not melted even after the predetermined time period has elapsed, depending on the degree of freezing of the throttle valve. In such a case, it is erroneously determined that the throttle valve has failed, and the electronic throttle control system is caused to go down, so that the throttle valve cannot be controlled thereafter. Further, if the predetermined time period is set to a still longer time period to avoid the above inconvenience, the motor for actuating the throttle valve is caused to be driven for a long time period in a state where the throttle valve has a difficulty in moving due to the frozen ice therearound. The heat thus generated by the motor may cause failure or a shortened service life of the motor.
It is an object of the invention to provide a throttle control system and method for an internal combustion engine as well as an engine control unit, which are capable of controlling a throttle valve without any trouble even when the throttle valve is frozen.
To attain the above object, according to a first aspect of the present invention, there is provided a throttle control system for an internal combustion engine, for controlling a degree of opening of a throttle valve arranged in an intake system of the engine,
the throttle control system comprising:
throttle valve opening-detecting means for detecting the degree of opening of the throttle valve;
target opening-setting means for setting a target degree of opening for control of the degree of opening of the throttle valve;
smallest opening-detecting means for detecting a smallest degree of opening of the throttle valve after a start of the engine;
throttle valve temperature-detecting means for detecting a temperature of the throttle valve; and
target opening lower limit value-setting means for setting a lower limit value of the target degree of opening to a degree of opening larger than the smallest degree of opening of the throttle valve when the detected smallest degree of opening is larger than a predetermined degree of opening and at the same time the detected temperature of the throttle valve is lower than a predetermined temperature.
According to this throttle control system, the smallest degree of opening of the throttle valve is detected, and when it is determined that the smallest degree of opening is larger than the predetermined degree of opening and at the same time the temperature of the throttle valve is lower than the predetermined temperature, the lower limit value of the target degree of opening of the throttle valve is set to a value larger than the detected smallest degree of opening. When the throttle valve is in such a low temperature condition as causes freezing thereof, the target degree of opening is set to a value larger than the smallest degree of opening. This prevents the throttle valve from abutting against frozen ice, whereby the throttle valve is controlled to the target degree of opening without any trouble. Further, when failure determination can be carried out based on the actual movement of the throttle valve, it is possible to positively prevent freezing of the throttle valve from causing an erroneous determination.
Preferably, the smallest degree of opening is a degree of opening of the throttle valve detected during control of the throttle valve to a fully closed position, at a start of the engine.
According to this preferred embodiment, a degree opening of the throttle valve detected during control of the throttle valve to a fully closed position at the start of the engine is set to the smallest degree of opening. Therefore, at the start of the engine, when the temperature of the engine is lower than the predetermined temperature, i.e. when it is estimated that the throttle valve is frozen, the advantageous effects as described above can be obtained.
Preferably, the throttle control system includes stuck state-detecting means for detecting a stuck state of the throttle valve, and the smallest degree of opening is an opening of the throttle valve detected when the stuck state-detecting means detects the stuck state of the throttle valve, after a start of the engine.
According to this preferred embodiment, a degree of opening of the throttle valve detected when the stuck state of the throttle valve is detected after the start of the engine is set to the smallest degree of opening. Therefore, when the engine is in such a low temperature condition as causes the freezing thereof, after the start of the engine, the advantageous effects as described above can be obtained.
For example, the predetermined degree of opening is a degree of opening of the throttle valve to be detected when the throttle valve is normally controlled to a fully-closed position.
Preferably, the predetermined degree of opening is set according to a learned fully-closed position value obtained by learning the degree of opening of the throttle valve detected when the throttle valve is controlled to a fully-closed position during a predetermined operation of the engine.
According to this preferred embodiment, the predetermined degree of opening used for determining whether or not the throttle valve is frozen is set according to the learned fully-closed position value obtained by learning the degree of opening of the throttle valve when the throttle valve is controlled to the fully-closed position. This makes it possible to accurately determine whether or not the throttle valve is frozen while causing changes in the operating characteristics of the throttle valve to be reflected on the determination.
Preferably, the throttle control system further comprises means for progressively degreasing the lower limit value of the target degree of opening from the degree of opening larger than the smallest degree of opening of the throttle valve as the temperature of the throttle valve detected by the throttle valve temperature-detecting means rises.
For example, the throttle valve temperature-detecting means detects at least one of a temperature of intake air and a temperature of coolant of the engine as the temperature of the throttle valve.
To attain the above object, according to a second aspect of the invention, there is provided a throttle control system for an internal combustion engine, for controlling a degree of opening of a throttle valve arranged in an intake system of the engine,
the throttle control system comprising:
a throttle valve opening-detecting module for detecting the degree of opening of the throttle valve;
a target opening-setting module for setting a target degree of opening for control of the degree of opening of the throttle valve;
a smallest opening-detecting module for detecting a smallest degree of opening of the throttle valve after a start of the engine;
a throttle valve temperature-detecting module for detecting a temperature of the throttle valve; and
a target opening lower limit value-setting module for setting a lower limit value of the target degree of opening to a degree of opening larger than the smallest degree of opening of the throttle valve when the detected smallest degree of opening is larger than a predetermined degree of opening and at the same time the detected temperature of the throttle valve is lower than a predetermined temperature.
According to the second aspect of the invention, the same advantageous effects as provided by the first aspect of the invention can be obtained.
Preferably, the smallest degree of opening is a degree of opening of the throttle valve detected during control of the throttle valve to a fully closed position, at a start of the engine.
According to this preferred embodiment, the same advantageous effects as provided by the corresponding preferred embodiment of the first aspect of the invention can be obtained.
Preferably, the throttle control system includes a stuck state-detecting module for detecting a stuck state of the throttle valve, and the smallest degree of opening is a degree of opening of the throttle valve detected when the stuck state-detecting means detects the stuck state of the throttle valve, after a start of the engine.
According to this preferred embodiment, the same advantageous effects as provided by the corresponding preferred embodiment of the first aspect of the invention can be obtained.
For example, the predetermined degree of opening is a degree of opening of the throttle valve to be detected when the throttle valve is normally controlled to a fully-closed position.
Preferably, the predetermined degree of opening is set according to a learned fully-closed position value obtained by learning the degree of opening of the throttle valve detected when the throttle valve is controlled to a fully-closed position during a predetermined operation of the engine.
According to this preferred embodiment, the same advantageous effects as provided by the corresponding preferred embodiment of the first aspect of the invention can be obtained.
Preferably, the throttle control system further comprises a module for progressively degreasing the lower limit value of the target degree of opening from the degree of opening larger than the smallest degree of opening of the throttle valve as the temperature of the throttle valve detected by the throttle valve temperature-detecting module rises.
For example, the throttle valve temperature-detecting module detects at least one of a temperature of intake air and a temperature of coolant of the engine as the temperature of the throttle valve.
To attain the above object, according to a third aspect of the invention, there is provided a throttle control method for controlling a degree of opening of a throttle valve arranged in an intake system of an internal combustion engine,
the throttle control method comprising the steps of:
detecting the degree of opening of the throttle valve;
setting a target degree of opening for control of the degree of opening of the throttle valve;
detecting a smallest degree of opening of the throttle valve after a start of the engine;
detecting a temperature of the throttle valve; and
setting a lower limit value of the target degree of opening to a degree of opening larger than the smallest degree of opening of the throttle valve when the detected smallest degree of opening is larger than a predetermined degree of opening and at the same time the detected temperature of the throttle valve is lower than a predetermined temperature.
According to the third aspect of the invention, the same advantageous effects as provided by the first aspect of the invention can be obtained.
Preferably, the smallest degree of opening is a degree of opening of the throttle valve detected during control of the throttle valve to a fully closed position, at a start of the engine.
According to this preferred embodiment, the same advantageous effects as provided by the corresponding preferred embodiment of the first aspect of the invention can be obtained.
Preferably, the throttle control method includes the step of detecting a stuck state of the throttle valve, and the step of smallest degree of opening is a degree of opening of the throttle valve detected when the stuck state of the throttle valve is detected in the step of detecting a stuck state, after a start of the engine.
According to this preferred embodiment, the same advantageous effects as provided by the corresponding preferred embodiment of the first aspect of the invention can be obtained.
For example, the predetermined degree of opening is a degree of opening of the throttle valve to be detected when the throttle valve is normally controlled to a fully-closed position.
Preferably, the predetermined degree of opening is set according to a learned fully-closed position value obtained by learning the degree of opening of the throttle valve detected when the throttle valve is controlled to a fully-closed position during a predetermined operation of the engine.
According to this preferred embodiment, the same advantageous effects as provided by the corresponding preferred embodiment of the first aspect of the invention can be obtained.
Preferably, the throttle control method further comprises the step of progressively degreasing the lower limit value of the target degree of opening from the degree of opening larger than the smallest degree of opening of the throttle valve as the detected temperature of the throttle valve rises.
For example, the step of detecting a temperature of the engine includes detecting at least one of a temperature of intake air and a temperature of coolant of the engine as the temperature of the throttle valve.
To attain the above object, according to a fourth aspect of the invention, there is provided an engine control unit including a control program for causing a computer to carry out control of a degree of opening of a throttle valve arranged in an intake system of an internal combustion engine,
wherein the control program causes the computer to detect the degree of opening of the throttle valve, set a target degree of opening for control of the degree of opening of the throttle valve, detect a smallest degree of opening of the throttle valve after a start of the engine, detect a temperature of the throttle valve, and set a lower limit value of the target degree of opening to a degree of opening larger than the smallest degree of opening of the throttle valve when the detected smallest degree of opening is larger than a predetermined degree of opening and at the same time the detected temperature of the throttle valve is lower than a predetermined temperature.
According to the fourth aspect of the invention, the same advantageous effects as provided by the first aspect of the invention can be obtained.
Preferably, the smallest degree of opening is a degree of opening of the throttle valve detected during control of the throttle valve to a fully closed position, at a start of the engine.
According to this preferred embodiment, the same advantageous effects as provided by the corresponding preferred embodiment of the first aspect of the invention can be obtained.
Preferably, the control program causes the computer to detect a stuck state of the throttle valve, and the smallest degree of opening is a degree of opening of the throttle valve detected when the stuck state of the throttle valve is detected, after a start of the engine.
According to this preferred embodiment, the same advantageous effects as provided by the corresponding preferred embodiment of the first aspect of the invention can be obtained.
For example, the predetermined degree of opening is a degree of opening of the throttle valve to be detected when the throttle valve is normally controlled to a fully-closed position.
Preferably, the predetermined degree of opening is set according to a learned fully-closed position value obtained by learning the degree of opening of the throttle valve detected when the throttle valve is controlled to a fully-closed position during a predetermined operation of the engine.
According to this preferred embodiment, the same advantageous effects as provided by the corresponding preferred embodiment of the first aspect of the invention can be obtained.
Preferably, the control program causes the computer to progressively degrease the lower limit value of the target degree of opening from the degree of opening larger than the smallest degree of opening of the throttle valve as the detected temperature of the throttle valve rises.
For example, the control program causes the computer to detect at least one of a temperature of intake air and a temperature of coolant of the engine as the temperature of the throttle valve.
The above and other objects, features, and advantages of the invention will become more apparent from the following detailed description taken in conjunction with the accompanying drawings.